Diodes AP1694A - Manual (Page 8)

AP1694A
Document number: DS37094 Rev. 1 - 2
8 of 15
www.diodes.com
May 2014
© Diodes Incorporated
AP1694A
A Product Line of
Diodes Incorporated
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Application Information Based on Buck Structure
The AP1694A uses constant on time control method within one AC cycle to achieve the high power factor. When the dimmer is connected to the
driver, although a part of input voltage is cut off by the dimmer, the system still operates as constant on time mode, in this way good dimmer
compatibility can be realized.
T1
OUT
+
VCC FB
OUT
CS GND
U1 AP1694A
C 3
R7
R5
R6
R4 D1
C4
R3
Q1
BD1
C1
L1
R8
D2
R1
RI
SGND
R2 R9
RF
L
N C2
Z1
Q2
F1
TVS1
Figure 1. Typical Buck Application Circuit
When the dimmer is connected, and the conduction angle of the dimmer is
  
, according to the control principle of the IC, the output current
can be got as below:
_
1
sin( ) 1
( , ) ( , ) 2 8
2
0
cs ref
o pk
V
if
I I R
else
  
   

   
   

（ ）
In consider of the dead zone of the buck structure, the output current DC value can be calculated as below:
_
0
1
( , )
o mean o
I k I d

  

  
Where,
_ cs ref
V
is the reference of the current sense, and the typical value is 1V.

is the cut off angle of dimmer.

is the phase of the input voltage.
k is the current modification coefficient , and the value is approximate to be 0.7.
When no dimmer is connected with the driver (
0
 
), the output current DC value can be got as:
s_ref
_
1
8
c
o mean
V
I k
R

  